The present invention relates generally to welding-type devices and, more particularly, to a high frequency transformer having a higher leakage inductance boost winding.
Welding, cutting, and heating systems often require a step-down of the primary or input power for the welding, cutting, or heating application. That is, primary or input power is typically supplied to the welding, cutting, or heating system at voltages ranging from 110 to 575. However, the desired output voltage is typically much lower. Generally, transformers, rectifiers, and filters are used to convert the input power to usable power for the welding, cutting, or heating application.
A transformer is typically used to reduce or increase the voltage of incoming power so that it is usable for the particular welding, cutting, or heating application. Transformers are typically made up of a primary and secondary windings, or coils, around a metal core. As such, the primary voltage, or input voltage, enters the primary winding and creates a magnetic field that induces voltage in the secondary winding. The secondary winding then yields a voltage that is usable for the welding, cutting, or heating application. Typically, a simple turns ratio determines the secondary voltage. For example, by dividing the number of turns and the primary winding by the number of turns in a secondary winding will determine the amount by which the input voltage is stepped down by the transformer. For example, a primary winding having 120 turns and operable at 240 volts may have a corresponding secondary winding having 12 turns that yield or output 24 volts. As such, the input voltage is stepped down by ten-fold.
High frequency transformers are particularly applicable to inverter-controlled power sources. In an inverter-controlled environment, the incoming power is first rectified to DC and then filtered for smoothness. The filtered DC power is then sent through one or more IGBT that converts it back to AC but at a very high frequency. This high frequency alternating current is then stepped down or stepped up by a transformer in a manner similar to that described above. A rectifier and filter then rectify the stepped down AC signal to a DC signal and filter the DC signal to produce smooth usable output power, respectively.
Some welding, cutting, and heating applications require a step-up of the input power. That is, for efficient operation of the welding, cutting, or heating system, it may be necessary to increase or convert the input line voltage to a higher line voltage using a transformer or converter. Boost transformers can typically raise the line voltage in the range of 5% to 25%. With boost converters or transformers, it is desirable to maximize the output voltage while conserving primary current under higher output current conditions.
A number of transformer configurations have been developed to maximize the output voltage while conserving primary current. One exemplary approach included an output transformer having a core, primary windings, and a two-section secondary winding. The output transformer also includes a first auxiliary winding connected to one of the secondary sections to create an auxiliary current pulse as the core of the transformer is magnetized. The transformer also includes a second auxiliary winding connected to the other of the secondary sections to create a second auxiliary current pulse as the core is re-magnetized. In this exemplary embodiment, the auxiliary windings are connected in series with the secondary windings section. However, these auxiliary windings are in series with current control circuits including current-limiting inductors thereby increasing the cost as well as complexity of the transformer.
It would therefore be desirable to design a transformer having a boost winding that is constructed in such a manner as to eliminate the need for a separate inductor in series with the boost winding. It is also desirable to design a transformer assembly with improved part-to-part consistency.
The present invention is directed to a high frequency transformer assembly having a boost winding with higher leakage inductance overcoming the aforementioned drawbacks. The present invention is particularly applicable for use with welding-type devices such as welders, plasma cutters, and induction heaters. The high frequency transformer has a primary winding, and preferably, two center tapped secondary or weld windings in parallel with a center tapped tertiary or boost winding. The two weld windings have half the turns ratio of the boost winding. All three windings are placed in parallel and together with a smoothing inductor form a welding output circuit. The aforementioned boost winding comprises four smaller sections such that each section resides on the outer legs of a ferrite E-core. Placement of the boost windings over the outer legs of the ferrite cores eliminates the need for a separate inductor in series with the boost winding. As indicated previously, a pair of secondary or welding windings are provided. Because two weld windings are used, the leakage inductance of the weld windings is reduced. Further, because the two weld windings carry an equal share of current, board-mounted discrete diodes may be used instead of more costly screw-top devices. The transformer also includes a bobbin designed to support the ferrite cores and the coil assemblies. Preferably, the bobbin includes a series of spacers that are used to guarantee consistent placement of the primary winding across the bobbin. This lowers the leakage inductance in the weld winding. Moreover, the spacers for the primary winding guarantee part-to-part consistency.
Therefore, in accordance with one aspect of the present invention, a high frequency transformer for a welding-type device is provided. The transformer includes a pair of ferrite cores and a bobbin configured to receive and support the pair of ferrite cores. A primary winding assembly, as well as, a secondary winding assembly is provided. The secondary winding assembly is in parallel with a center topped tertiary winding assembly. The tertiary winding assembly includes a number of coil sections such that each coil section is wrapped around an outer leg of a ferrite core.
In accordance with yet another aspect of the present invention, an apparatus configured to manage and condition power for a welding-type device includes a housing forming an enclosure having a fore end and an aft end. The apparatus includes a front panel connected to the housing at the fore end and a rear panel connected to the housing at the aft end. A plurality of electrical components is disposed within the enclosure wherein the components include a transformer assembly. The transformer assembly includes a pair of multi-pole ferrite cores and a bobbin configured to receive and support the ferrite cores. The transformer assembly also includes a primary winding, at least one weld winding, and a boost winding. The windings are in electrical parallel and collectively form a welding output circuit. The boost winding includes a number of sections such that each section is positioned over an outer pole of a ferrite core. The apparatus further includes a cable extending through the rear panel and configured to supply raw power to the apparatus.
In accordance with a further aspect of the present invention, a kit for retrofitting a transformer assembly of a welding-type device is provided. The kit includes a pair of multi-pole ferrite cores and a bobbin configured to support the pair of multi-pole ferrite cores. A primary winding as well as at least one weld winding is also provided. The kit further includes a boost winding having a number of coil sections wherein each coil section is configured to be positioned around an outer pole of a ferrite core.
Various other features, objects and advantages of the present invention will be made apparent from the following detailed description and the drawings.